<b_jonas> slashlearn euclid//Euclid is a short geeky game in which the goal is to do Euclidean compass and straightedge constructions in as few steps as possible. It runs in the browser, found at "http://www.euclidthegame.com/". It was popular among #esoteric regulars in 2016-07.

'Collatz problem calculator
'Programmed by Jannis Harder (jix), 2005
1[1?,1~10:2,0>-1,2=*0,2>-2,0+*2,0+*1,0-48]1
2[0#,5=10,5$,0~1:0,1=*0,1|1,1<-1:3,0>1]2
3[1=*0,0+*1,0+*1,0+1]2